Case Report Cystic Midline Posterior Fossa Lesion in a Young Adult

We report the case of a 28-year-old male who presented with progressive vertigo, occipital headache, and tandem gait instability. Brain MRI revealed a well-defined, cystic lesion in the superior vermis with a solid, enhancing nodule, causing compression of the fourth ventricle and mild obstructive hydrocephalus. Imaging findings were highly suggestive of cerebellar hemangioblastoma. The case highlights the importance of advanced neuroimaging in the preoperative differential diagnosis of posterior fossa tumors.

• Patient: Male, 28 years old
• Symptoms: Horizontal nystagmus, occipital headache, unsteady tandem gait, vertigo, and nausea. No sensorimotor deficits or seizures.
• Neurological exam: Alert, oriented, afebrile. Horizontal nystagmus to the left, positive Romberg, unstable tandem gait. No focal deficits.

MRI Brain

• Technique: MRI with and without IV contrast, including perfusion sequences and full spinal axis T1 sagittal imaging.

Axial T1-weighted MRI image following intravenous gadolinium administration.

Axial T2 FLAIR MRI image

Lesion Characteristics:

• Well-circumscribed cystic lesion in the superior cerebellar vermis: ~45 × 35 × 35 mm
• Solid mural nodule: 12 × 6 × 6 mm (superior margin)
• Cystic component: fine septations, no contrast enhancement
• Solid nodule:
  • Intense contrast enhancement
  • High rCBV (5.8) with <50% signal recovery
  • Facilitated diffusion
  • T2 hypointense foci (possible flow voids)

Additional Findings:

• Mild vasogenic edema in cerebellum and right middle cerebellar peduncle
• Mass effect on 4th ventricle and anterior brainstem displacement
• Partial obliteration of basal cisterns
• Mild obstructive hydrocephalus (Evans index 0.28)
• No transtentorial or tonsillar herniation
• Spinal axis MRI: No evidence of drop metastases or secondary lesions

• Most likely: Hemangioblastoma
• Differential diagnosis: Pilocytic astrocytoma (less likely due to perfusion features)

• Surgical resection planned
• Corticosteroid therapy initiated
• Preoperative thoracoabdominopelvic imaging completed
• Awaiting histopathological confirmation

Posterior fossa cystic tumors with mural nodules in young adults commonly include hemangioblastoma and pilocytic astrocytoma. Key imaging features suggesting hemangioblastoma are: vascular nodule, high rCBV, and facilitated diffusion. These features aid in presurgical planning and help reduce intraoperative risk.

A cystic lesion in the cerebellar vermis with an enhancing mural nodule, high perfusion, and facilitated diffusion strongly suggests hemangioblastoma. Advanced imaging is essential for accurate differential diagnosis and surgical strategy.

posterior_fossa, hemangioblastoma, pilocytic_astrocytoma, cerebellum, mri_perfusión, young_adult